Nanostructuring of NiMnSb(110): Influence on surface magnetic properties

The magnetic properties, crystal structure, and topography at the (110) surface of the ferromagnetic half-Heusler alloy NiMnSb have been investigated by means of magneto-optical Kerr effect, spin-resolved appearance potential spectroscopy, low-energy electron diffraction, and atomic force microscopy. A standard sputter-anneal cleaning procedure leads to a nanostructuring of the surface with consequences for the magnetic properties. This finding sheds light on the reduced spin polarization measured by surface-sensitive techniques on NiMnSb surfaces.

Figure 1

(Color online) MOKE hysteresis loops of NiMnSb(110). The magnetic field was applied along a ⟨111⟩ crystallographic direction. (a) Extra situm measurement after crystal polishing. (b) In situ measurement after many cycles of ${\mathrm{Ar}}^{+}$ ions bombardment and annealing.

Figure 2

(Color online) LEED patterns of NiMnSb(110), recorded at $58\mathrm{eV}$ (a) and a few eV above $58\mathrm{eV}$ (b), at $85\mathrm{eV}$ (c) and a few eV above $85\mathrm{eV}$ (d). Open circles in (b) and (d) represent the LEED spots recorded at 58 and $85\mathrm{eV}$, respectively, taken from (a) and (c). The split spots move in ⟨100⟩ and ⟨110⟩ crystal directions. They are interpreted as LEED patterns from facets with {111} and {100} surface orientations (see text). The numbers indicate the coordinates of the reciprocal lattice points associated with the LEED spots.

Figure 3

(Color online) AFM pictures of three different regions of the NiMnSb(110) sample. (a) Nonsputtered region. (b) Slightly sputtered region [about half as much as in (c)]. (c) Heavily sputtered region. The lateral size of the pictures is equivalent to $5\mu \mathrm{m}$. The bars on the right indicate the height of the structures.